1. Field of the Invention
The present invention relates to an ignition apparatus chiefly used to run an internal combustion engine, and more particularly, to an ignition coil apparatus for high-frequency discharge employed in an ignition apparatus for a spark-ignited internal combustion engine.
1. Background Art
Problems are arising in terms of environmental conservation and depletion of fuel in recent years and it is urgently necessary for the automobile industry to address these problems. As an example of an effort in addressing these problems, there is a method of markedly improving fuel consumption by means of engine downsizing and weight saving with the use of a supercharger.
It is known that in a highly supercharged state, an internal pressure of an engine combustion chamber rises extremely high even when fuel is not burning and it therefore becomes difficult to generate a spark discharge to start combustion. One of the reasons underlying this difficulty is that a required voltage to trigger a breakdown between a high-voltage electrode and a GND electrode (gap) of a spark plug becomes so high that it exceeds a withstanding voltage value of an insulator portion of the spark plug.
A study to increase the withstanding voltage of the insulator portion is being conducted to solve this problem. It is, however, difficult to ensure a withstanding voltage sufficiently high for the required voltage in the actual condition. Under these circumstances, there is no other countermeasure than to narrow a gap spacing of the spark plug.
Narrowing the gap of the spark plug, however, increases influences of an anti-inflammatory action by the electrode portion in turn. Hence, there arises another problem that start-up performance and combustion characteristics become poor.
This problem may be eliminated by avoiding such influences, more specifically, by providing more energy than thermal energy consumed by the anti-inflammatory action, that is, at the electrode portion with a spark discharge or by allowing combustion to take place at the remotest point from the electrode. For example, an ignition apparatus disclosed in Patent Document 1 is proposed.
The ignition apparatus disclosed in Patent Document 1 is an apparatus capable of generating a high-energy spark discharge and forming a discharge plasma spreading in a wider range than that by a normal spark discharge by generating a spark discharge across a spark plug gap using an ignition coil in the related art and by flowing a high-frequency current into a path of the spark discharge via a diode and a mixer.